JPS62236146A - Optical pick-up - Google Patents

Abstract

PURPOSE:To easily detect the position dislocation direction of a lens for adjusting a focus by forming at least two light emitting parts at a semiconductor laser element, and setting these light emitting parts by making respective light emitting shafts mutually parallel and dislocating the position backward and forward on the light emitting shafts. CONSTITUTION:Laser light 10 and 11 are photodetected by photo diodes 8 and 9, and a high frequency signal (RF signal 1 and RF signal 2) to extract the alternating current component of the photodetected light signal is sent to an electronic circuit as a reading signal from the recording surface of a disk 5. When the code of the signal of the difference is confirmed by obtaining the difference signal between the RF signal 1 and the RF signal 2, it can be easily judged whether or not a lens 4 is dislocated and positioned to any backward and forward sides on the light emitting shaft. Consequently, in an optical pick-up 1, by making the difference signal into a focus error signal, a focus servo can be operated so as to correct the position location of the lens 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup that reads signals from a disk or the like by utilizing the self-coupling effect of a semiconductor laser.

[Prior art]

Optical pink-up, which uses the self-coupling effect of semiconductor lasers to read signals, is generally 5000P (Se
lf Coupled 0ptical Pic
kup).

This type of optical pickup 21, as shown in FIG.
A lens 23 that focuses laser light 26 is disposed between one semiconductor laser element 22 and a disk 24 serving as a recording medium so as to be movable in the optical axis direction of this laser light.

Further, a photodiode 25 is arranged at the light emitting section of the rear mirror surface of the semiconductor laser element 22, facing the light emitting section thereof. When the optical pickup 21 described above reads the recording on the disk 24, the semiconductor laser element 22 is operated with a constant current, and the laser beam 26 is projected onto the disk 24 from the light emitting part of the semiconductor laser element 22. Laser light 26 projected from semiconductor laser element 22 is focused onto the recording surface of disk 24 by lens 23 and then reflected.

This reflected laser light 26 is again focused by the lens 23 and then enters the light emitting portion of the semiconductor laser element 22 .

At this time, due to the self-coupling effect, the semiconductor laser element 22 outputs from the light emitting part on the rear mirror surface of the semiconductor laser element 22 based on the incident laser light 26, so this output light 27 is received by the photodiode 25. Then, a high frequency signal (hereinafter referred to as RF) is obtained by extracting the alternating current component of the received optical signal.
The double signal) is read from the recording surface of the disk 24 and sent to the electronic circuit as a read signal. As a result, the optical pickup 21 reads the recording on the disc 24. Other known signal reading methods using the 5-coop system include a method of reading a change in optical output from the front mirror surface of a semiconductor laser, a method of reading a change in resistance, and the like.

Incidentally, in the optical pickup 21 shown in FIG. 5, the relationship between the position Z of the lens 23 and the above-mentioned RF multiplied signal amplitude is as shown in FIG. In this case, the position Z0 of the lens 23 indicating the peak of the RF multiplied signal amplitude indicates the just focus position of the optical pink-up 21. That is, when the lens 23 is located at these 20 points, the laser beam 26 emitted from the semiconductor laser element 22 is directed toward the disk 2.
The reflected light from the disk 24 is focused on the light emitting point of the semiconductor laser element 22. For this reason, the optical system is usually arranged so that the lens 23 is located at 20 points where the RF multiplied signal is maximum.

However, in the conventional structure described above, the position of the lens 23 is
If the RF multiplication signal amplitude is shifted from the zero point, this RF
Although it is possible to detect from the multiplication signal that the position of the lens 23 has deviated from the 20th point, it is not possible to detect which side of the 20th point the position of the lens 23 has deviated from. Therefore, there was a drawback that it was impossible to determine in which direction the focusing servo for correcting the position of the lens 23 at 20 points should be operated.

[Purpose of the invention]

The present invention has been made in consideration of the above-mentioned conventional problems, and provides an optical pickup that uses the self-coupling effect of a semiconductor laser to read signals. The object of the present invention is to provide an optical pickup that can easily detect the direction of positional shift.

[Structure of the invention]

In order to achieve the above object, an optical pickup according to the present invention focuses light emitted from a light emitting part of a semiconductor laser element onto an optical recording medium via a lens movably disposed on a light emitting axis. The light reflected from this recording medium, which becomes a read signal, is again focused on the light emitting part of the semiconductor laser element through the lens, and based on this, the light that becomes a read signal is generated from the light emitting part of the rear mirror surface of the semiconductor laser element. In an optical pickup that obtains an output light of
The light emitting axes are set parallel to each other and shifted back and forth on the light emitting axes, so that the amplitudes of the signals extracted from the reflected light from the optical recording medium of the light emitted from each of the light emitting parts are different. The present invention is characterized in that the direction of positional shift of the lens can be detected using the following.

In addition to the servo in the direction of the light emission axis (so-called focus servo) provided by the present invention, the optical pickup requires a servo in the direction perpendicular to the light emission axis (tracking servo or tangential servo). Also in the optical pickup of the present invention, a conventional method such as the wobbling method may be used for the servo in the direction perpendicular to the light emitting axis.

〔Example〕

An embodiment of the present invention will be described below based on FIGS. 1 to 4.

As shown in FIG. 1, the optical pickup 1 has a semiconductor laser element 2 on the emission axis of the semiconductor laser elements 2 and 3 between the two semiconductor laser elements 2 and 3 and a disk 5 serving as a recording medium. - A lens 4 that focuses the laser beams 6 and 7 emitted from the lens 3 is arranged so as to be movable in the direction of the light emission axis. The above two semiconductor laser elements 2.
3, the light emitting axes are parallel to each other, and each light emitting part is arranged at a position shifted by a predetermined distance a back and forth in the direction of the light emitting axis. Photodiodes 8 and 9 are arranged in the light emitting portions of the rear mirror surfaces of the semiconductor laser elements 2 and 3, respectively, and are arranged opposite to them. It is configured to be able to detect the output light from the section.

In the above configuration, when the semiconductor laser elements 2 and 3 are operated with a constant current, laser beams 6 and 7 are emitted from the light emitting parts toward the disk 5, respectively. These laser beams 6 and 7 are
After being focused onto the recording surface of the disk 5 by the lens 4,
reflect. The reflected laser beams 6 and 7 serving as read signals from the disk 5 are again focused by the lens 4 and enter the light emitting portions of the semiconductor laser elements 2 and 3. Based on the incident laser beams 6 and 7, the semiconductor laser elements 2 and 3
Laser beams 10 and 11 are output from the light emitting section on the rear mirror surface of the mirror. These laser beams 10 and 11 are transmitted through a photodiode 8
・The high frequency signals (hereinafter referred to as RF signal 1 and RF signal 2) obtained by extracting the alternating current components of the received optical signals are sent to the electronic circuit as signals read from the recording surface of the disk 5. sent to.

With this configuration, the relationship between the position Z of the lens 4 and the RF signals 1 and 2 is as shown in FIG. 2(a).
It becomes as shown in . The vertical axis of the graph in Figure 2 (a) is RF
The amplitudes of the signal 1 and the RF signal 2 are shown, and the horizontal axis shows the position Z of the lens 4.

In the figure, when the lens 4 is at the 21st point, the RF signal 1 has the maximum value, and when the lens 4 is at the 22nd point, the RF signal 2 has the maximum value. This is because the positions of the semiconductor laser elements 2 and 3 are shifted back and forth on the emission axis, and the laser beams 6 and 7 emitted from each semiconductor laser element 2 and 3 are directed onto the recording surface of the disk 5 by the lens 4. This is due to the difference in the position of the lens 4 that can best focus the light. This makes it possible to detect which side of the light emitting axis the lens 4 is deviated from, forward or backward, based on the two signals whose maximum values are deviated. Specifically, as shown in FIG. 2(b), for example, by obtaining a difference signal between RF signal 1 and RF signal 2 through an electronic circuit, and confirming the sign of this difference signal, the lens 4 It is possible to easily determine which side of the light-emitting axis the light-emitting axis is shifted from, forward or backward. Therefore,
In the optical pickup 1, by using this difference signal as a focus error signal, the focus servo can be operated to correct the positional deviation of the lens 4. It is best to set the position of the lens 4 at a position where the difference signal is O, but in this position, the RF signal 1
and RF signal 2 do not have the maximum amplitude.

However, in practice, it is difficult to set the amplitudes of both the RF signal 1 and the RF signal 2 to an amplitude level that can be used as an optical pickup at the position of the lens 4 where the difference signal is O. - This can be achieved by arbitrarily selecting the positional deviation distance a on the light emitting axis of the light emitting section 3.

Note that the present invention applies to the two semiconductor laser elements 2 and 3 described above.
For example, as shown in FIG.
A convex portion 13 and a concave portion 1 are formed in the light emitting portion of the semiconductor laser device 12.
4 is formed, thereby forming two light emitting parts that are shifted forward and backward with respect to the light emitting axis direction, and the convex part 13 and the concave part 1
It is also possible to use a so-called laser array configured to emit laser light from each of the four laser beams. Further, as shown in FIG. 4, a transparent body 17 having a different refractive index, such as a glass plate, is placed in front of one of the two light emitting parts 16a and 16b formed in one semiconductor laser element 15. may be arranged so that the laser beams emitted from the light emitting sections 16a and 16b are optically shifted in position.

〔Effect of the invention〕

As described above, in the optical pickup of the present invention, at least two light emitting parts are formed in a semiconductor laser element, and these light emitting parts are set so that their light emitting axes are parallel to each other and are shifted back and forth on the light emitting axis. This is the configuration. As a result, even if the position of the lens disposed between the semiconductor laser element and the optical recording medium deviates from the just focus position, at least two light emitting parts whose light emission positions are deviated back and forth on the light emission axis can be used. This makes it possible to detect the direction of lens displacement using the signal extracted from the read signal. Therefore, it is possible to accurately operate the focus servo for correcting the lens position by using the extracted signal as a focus error signal.

[Brief explanation of drawings]

1 and 2 show an embodiment of the present invention, and FIG. 1 is an explanatory diagram showing the schematic configuration of an optical pickup;
FIGS. 2(a) and (b) are graphs showing the relationship between the amplitude of the read signal and the lens position, FIGS. 3 and 4 are schematic explanatory diagrams showing other embodiments of the light emitting part in the semiconductor laser device, 5 and 6 show a conventional example, in which FIG. 5 is an explanatory diagram showing the schematic configuration of an optical pickup, and FIG. 6 is a graph showing the relationship between the amplitude of the read signal and the lens position. . 1 is an optical pickup, 2, 3, 12, and 15 are semiconductor laser elements, 4 is a lens, and 5 is a disk (optical recording medium).
, 8 and 9 are photodiodes. Figure 1, P$2 (a) Figure, ＼ Figure 5 Fu

Claims (1)

[Claims] 1. The light emitted from the light emitting part of the semiconductor laser element is focused on an optical recording medium through a lens movably placed on the light emitting axis, and the light reflected from this recording medium, which becomes a read signal, is collected again. In the optical pickup, the light is focused on the light emitting part of the semiconductor laser element through the lens, and based on this, output light is obtained as a read signal from the light emitting part of the rear mirror part of the semiconductor laser element. An optical pickup characterized in that two light emitting sections are formed, and these light emitting sections are set so that their light emitting axes are parallel to each other and are shifted back and forth on the light emitting axis.